1. Field of the invention
The present invention relates to a hydrodynamic clutch and a method of operating a hydrodynamic clutch.
2. Description of the related art
Hydrodynamic clutches for transfer of torque are known from many descriptions, for example from the pamphlets
1.) CR 252; and
2.) J. M. Voith GmbHxe2x80x9d xe2x80x9cHydrodynamic in drive technology; Vereinigte Fachverlage Krauskopf Ingenieur Digest; Mainz 1987. Hydrodynamic clutches for transfer of torque include at least two blade wheels arranged concentrically to each other. The two blade wheels include one primary blade wheel and a secondary blade wheel which, together, form at least one torus-shaped work chamber. The primary blade wheel acts as a pump impeller and the secondary blade wheel as a turbine wheel. The primary blade wheel is linkable with a drive shaft that can be coupled at least indirectly with a drive motor for torsional strength. The secondary blade wheel is linkable with a drive shaft that can be coupled at least indirectly for torsional strength with a machine that is to be driven. For the transfer of torque, the working chambers are to be filled with operating medium. The operating medium is circulated due to the primary blade wheel rotation during the operation of the clutch, and produces a reaction moment on the blading of the secondary blade wheel. This circulation of the operating medium between the primary and secondary blade wheels is also referred to as operating circulation. However, not the entire flow of energy is converted into reaction moment, only a part, while the remainder is converted into heat.
Cooling of the operating medium during operation of the clutch can be accomplished in various ways. Possible is a cooling circuit which is allocated to the operating circuit, and through which, during operation, a part of the operating medium would be continuously supplied. Through appropriate openings in the blade wheels and through nozzles, the heated operating medium could, for example, be admitted to a pump shell that is rotating at the speed of the primary blade wheel. There, the operating medium is received by a dynamic pressure tube which is positioned against the direction of rotation. In its fitting position, the dynamic pressure tube engages in the pump shell above the clutch shaft. Because of the pressure conditions, the flow energy of the operating medium which is accepted through the accumulation dynamic pressure tube is sufficient to return it again to the clutch, without additional help, through a cooling unit, a cooler or a heat exchanger. For this purpose, an enclosed coolant circuit is assigned to the operating circuit during operation. There is always a sufficient quantity of operating medium in the clutch and in the cooling circuit when stationary. No liquid is added to or removed from this circuit. By adding to or removing operating medium from the clutch, an increase or decrease of the motor speed is achieved. For this purpose, a supply line or channel and a discharge line or channel are assigned to the operating chambers for the purpose of filling and emptying. The supply and discharge lines are connected to an external operating medium supply source, such as an operating medium tank. The provision of the supply and discharge lines to the operating chambers can be arranged separately from the cooling circuit or by utilizing the lines or channels of the cooling circuits.
Other methods of exchanging or cooling the operating medium present in the operating chamber are possible. For example, the operating medium can be exchanged in the operating circuit by simultaneous removal of a certain volume of heated operating medium and by feeding of operating medium at lower temperature in the corresponding volume.
A significant problem with hydrodynamic clutches is that, depending on the application, and due to the rotation of the rotor parts of the clutch in a housing, the danger exists during start-up or activation of not filling the clutch to an exact level. Rather, the clutch can be overfilled, since an exact filling degree is very difficult to achieve. A deterioration of the efficiency level and an increasing leakage in the individual labyrinths, that is, the operating medium carrying lines, are apparent due to additional losses in the rotor parts themselves, such as the individual blade wheels, the housing and the rotor parts. A solution for the avoidance of these disadvantages, which would include an additional discharge line from the housing to the tank, is not desirable. In order to avoid overfilling, the supply line or the control unit for regulating the supply is triggered through a filling signal. The pressure in the discharge line, for example, may act as the filling signal. This pressure is measured by an acquisition sensor measuring the current pressure value in the discharge line from the operating chamber. The unit is locked electrically through a pressure switch when the unit exceeds a certain pressure so that supply of additional operating medium is prevented. However, the problem with such a method is that this signal is very inexact due to the varying marginal values. Also, this signal is often insufficient in order to prevent overfilling of the clutch. The pressure switch itself must always be adjusted very precisely during initial operation and, moreover, is subjected to the pressure peaks by the opened filling valve in the supply line. Specifically, a certain pressure value is continuously determined, with the device for measuring the pressure, during a time span between an empty condition of the clutch to a maximum filling of the clutch.
This pressure value steadily increases. A clear deviation in increase in a characteristic curve for the pressure, in dependence on the clutch filling, occurs only in the area of overfilling, that is at a clutch filling degree of greater than 100%. Each pressure value is therefore proportional to a certain filling degree. In order to determine a full status, a corresponding pressure value must therefore be measured. Tolerances may be included in these determinations. Consequently, only a small pressure area remains in which an overfill may be concluded. Within this limited pressure area, triggering of the pressure switch is necessary. Since the determined pressure value in the line can still be affected by a series of additional marginal factors, the acquired pressure value often does not correspond with the theoretically assigned filling degree. An early termination of filling at a filling degree of less than 100%, or overfilling, is then the result.
The present invention expands on a method of operating a hydrodynamic clutch so that the disadvantages of the current state of the art are avoided. Specifically, an effective protection against overfilling is realized which is suitable for different applications and offers quick response times. The method of the present invention distinguishes itself through low constructional and control engineering costs. The constructional design necessary in order to realize overfill protection is greatly non-susceptible to failure and is able to very quickly and precisely sense and respond to a maximum permissible filling degree. The maximum permissible filling degree can be consistent with the generally maximum permissible and freely definable filling degree.
According to the invention, a hydrodynamic clutch, including at least two blade wheels, one primary blade wheel and a secondary blade wheel, which together form at least one torus-shaped operating chamber, is operated so that only two filling degree conditions are recognized. One filling degree condition includes the condition of non-filling and partial filling, and a second filling degree condition describes the maximum permissible filling degree. An established first, very low first pressure value is assigned to the first filling degree condition. A greater pressure value is assigned to the second filling degree condition. The operating chamber is coupled with an accumulation chamber. The operating medium is fed from the operating chamber into the accumulation chamber at a certain ratio to the fill degree of the clutch. The operating medium level in the accumulation chamber is measured by a dynamic pressure sensor. This sensor is at least indirectly coupled with a device to influence the supply volume into the operating chamber, generally with a control device of a valve arrangement. The dynamic pressure sensor works, so to speak, according to the black-white principle. In the first filling degree condition, no pressure is sensed, or only a very small, substantially constant pressure is sensed. A substantially greater pressure is sensed in a second filling degree condition as compared to the first filling degree condition. The device for at least indirectly influencing the supply volume, generally an actuator of a valve arrangement in a supply line, is triggered only after the increased pressure occurs, thereby reducing or discontinuing the operating medium supply. In the method according to the invention, therefore, a corresponding pressure signal is allocated only to the operational conditions of no or partial filling, and full level filling. The pressure signal is generated through the dynamic pressure generator or sensor unit from the dynamic pressure occurring in the accumulation chamber. It is important that a refined, easily recognizable signal spike is generated during the transition from one state to another. This ensures that, regardless of additional disturbances during operating medium supply, overfilling is very easily recognized. This system is particularly not susceptible to pressure peaks through the filling valve that serve to influence the supply volume. A precise adjustment of the pressure switch during initial operation is unnecessary. Optimization of the system is unnecessary. The method distinguishes itself through an easily realizable and precise determination of exceeding a maximum filling degree by the use of a so-called black-white recognition.
As a rule, the maximum permissible filling degree is consistent with the actual maximum permissible filling degree. Generally, this is at 100%. It is, however, also possible to define the maximum permissible filling degree such that it corresponds to a predetermined filling degree that must be maintained for a particular application purpose. This filling degree, which must be maintained, may be described by any partial filling, specific to the maximum permissible filling degree.
In this device, the actual operating chamber is equipped with a catch trough which forms an accumulation chamber which is at least indirectly coupled with the operating chamber for the purpose of operating medium supply. The catch trough is arranged on a diameter which, during the operation of the hydrodynamic clutch, permits at least one filling of the accumulation chamber which is in proportion to the fill condition of xe2x80x9cfullxe2x80x9d in the hydrodynamic clutch. A dynamic pressure sensor is inserted into the accumulation chamber which is in communication with the operating chamber and which is formed by the catch trough. Preferably, the dynamic pressure sensor is in the form of a dynamic pressure tube for the purpose of sensing the fill level in the pressure chamber. The dynamic pressure generator, dynamic pressure tube, or sensor is located relative to the pressure chamber so that its opening is above or outside the operating medium fill level in the accumulation chamber when working with a non-filled or only partially filled clutch. Thus, its opening is not filled during this filling degree condition. Under these conditions, no operating medium is discharged through the dynamic pressure tube, and therefore no pressure signal is produced. However, as soon as the filling degree of the clutch reaches the maximum permissible filling degree, that is, generally full level, the accumulation chamber fills so that the dynamic pressure sensor, particularly the dynamic pressure tube with its opening, projects into the operating medium, picks up operating medium and thereby produces a signal for a dynamic pressure of Pdynamic=(xcfx81/2)xv2.
The dynamic pressure tube is located in the pressure chamber so that it acquires a high dynamic pressure only at an operating medium level in the accumulation chamber that is consistent with the maximum filling degree of the clutch. During the previous filling degree conditions which are consistent with empty or partial fill, the opening of the dynamic pressure tube is in an area of the accumulation chamber that is free of operating medium. Under these conditions, no pressure, or only a very low pressure, is measured through the dynamic pressure generator or sensor. A corresponding signal is produced. This low pressure is consistent, for example, with the pressure that would exist in an empty, open tube located in the atmosphere. Since in the area between the empty condition of the hydrodynamic clutch and the maximum filling degree no pressure signal and only a very low pressure is produced, and a dynamic pressure consistent with Pdynamic=(xcfx81/2)xv2 in the accumulation chamber is measured only when the maximum filling degree is reached, the condition of maximum filling degree in the hydrodynamic clutch can be recognized easily, immediately, and without error influences. This is because a differentiation is made only between the two filling degree conditions which differ by a strong pressure change in the form of a pressure increase. The resulting pressure signal may then be used to directly trigger a control device, specifically an actuation of a valve arrangement of a device to at least indirectly influence the through-flow volume in the supply to the operating chamber of the hydrodynamic clutch.
The maximum filling degree may correspond to an actual, maximum permissible filling degree of generally 100%. It is, however, also possible to define the maximum permissible filling degree such that it corresponds to a predetermined filling degree that must be maintained for a particular application purpose. The maximum filling degree which is consistent with the projected filling degree that is to be maintained can then be defined lower through each filling degree than the actual maximum permissible filling degree.
The definition of the filling degree to be maintained may be accomplished by adjusting the position of the dynamic pressure generator or sensor, specifically the opening for intake of operating medium in the accumulation chamber. It can be moved vertically, that is, in mounting position, radially. It can also be moved circumferentially in the accumulation chamber, or by pivoting. The entire circumferential area may be considered an adjustment area. The change in position for individual applications may be permanently set, or may be adjusted during operation. This offers the advantage that due to an overfill protection, various applications of a hydrodynamic clutch of a certain type and size are covered by active adaptability to changing requirements.
An advantageous design dispenses with a separate catch trough and utilizes the operating medium catch trough. This offers the advantage that already existing components are used. The location of the dynamic pressure tube in the operating medium trough, or protrusion of the end of the pressure tube into the operating medium trough, whereby the dynamic pressure tube is located in a separate fill segment which is located upstream from the operating medium catch trough, depends on the fact that draining from the operating medium trough occurs only as long as the maximum fill, that is, the full condition, has not yet been reached.
A multitude of possibilities present themselves for the arrangement of the accumulation chamber, which is substantially determined by the catch trough, and the assignment of the catch trough to the operating circuit. The catch trough may be designed as a separate component which is detachably linked with the corresponding rotor parts for assignment to the operating chamber. Preferably, however, the catch trough is manufactured with a blade wheel as a single component.
The dynamic pressure generator or sensor, which is preferably designed as a dynamic pressure tube, exhibits a part including an opening. This part is preferably located substantially parallel to the operating medium level establishing itself in the accumulating chamber. An inclined or vertical arrangement is also possible. The opening area extends at least partially vertical to the radial direction and in circumferential direction, whereby the direction of rotation must be considered. Preferably, the opening area points completely in circumferential direction and is arranged substantially vertical to it.
The method according to the invention may be utilized with all types of hydrodynamic clutches with variable filling. The clutches may take the form of single circuit clutches that are equipped with a primary and a secondary blade wheel and which together form a torus-shaped operating chamber. Alternatively, they may take the form of multiple circuit clutches on which several primary and secondary blade wheels form a multitude of operating chambers. In the first referred to arrangement, the catch trough may be assigned to the primary as well as the secondary blade wheel, or to a shell. In the last mentioned arrangement, an assignment to only one of the blade wheels, generally the outer blade wheel, is possible due to design factors.
The coupling between the accumulation chamber and the operating chamber may take various design forms. The connection between the interior of the catch trough and the operating chamber can preferably be accomplished through at least one clearance opening in the blade wheel. The clearance opening permits a transfer of operating medium from the operating chamber into the accumulation chamber. The clearance opening may vary in its configuration. Clearance openings in the form of clearance bores or elongated holes which are arranged on a determined diameter of the blade wheel are possible. Preferably, a multitude of openings are arranged on a diameter in circumferential direction. An arrangement of different diameters and/or a combination of the individual types of clearance openings is also possible.
The clearance openings may be located between the individual blades in the blade base or in an area, located radially inside the blade wheel, which is free of the blading. Depending on the design of the clearance opening, the fill may also be dependent on the speed differential, that is, the slippage between the primary and the secondary wheel. Thus, a short bridging of the pressure signal may be necessary.
Preferably, the part of the dynamic pressure tube that is equipped with the opening is arranged substantially parallel to the operating medium in the accumulation chamber. The opening itself may be placed vertically or inclined relative to the operating medium level. Independence from the direction of rotation is achieved by the provision of at least two pressure tubes which, with regard to the orientation of the part of the dynamic pressure tube that is equipped with the opening, are arranged in opposite direction. The two pressure tubes can be coupled with each other by use of a return valve. Another design form provides two dynamic pressure tubes which are coupled with each other with a separate respective pressure switch. The dynamic pressure tubes submerge in the accumulation chamber which is established by the catch trough and the outer dimensions of the blade wheel to which the catch trough is assigned. Thus, at a maximum filling degree, a dynamic pressure is measured by submerging the dynamic pressure tube in the operating medium in the catch trough. This maximum filling degree does not necessarily have to be consistent with the total fill condition. Any optional filling degree which can be defined as the maximum filling degree is also possible. This maximum filling degree may be defined according to the individual application of the hydrodynamic clutch. The dynamic pressure tube may be designed adjustably for this purpose, so that the height of immersion into the operating medium in the catch trough may be varied. This offers the advantage of being able to easily adapt overfill protection to different requirements. A design of the component that is equipped with the opening in radial direction is also possible.
The catch trough may, as already mentioned, be designed as a separate trough on the clutch rotor. However, there is also the option of utilizing the operating medium infeed trough, that is, the trough that is coupled with the supply line, for the purpose of supply to the operating chamber. In the last mentioned arrangement, no additional design measures are necessary on the blade wheels of the hydrodynamic clutch, but there is instead the possibility of utilizing existing devices.
The pressure signal produced by the dynamic pressure tube, which is used to trigger a control element in a device intended to influence the filling degree, especially a device for controlling the supply volume into the operating chamber, may be processed by an overriding control unit. Another method would be to direct triggering of the control element via the device for measuring a value which at least indirectly characterizes the filling degree of the clutch. To that effect, a control device becomes effective in that filling is either interrupted or reduced. Since the pressure signal is generally not effective directly on the control device, a converter to convert the pressure signal into an electric control signal is necessary between the device for measuring the filling degree. Preferably, a pressure switch is provided for this.
The method according to the invention for realizing overfill protection by recognizing the filling degree conditions can be used on all types of hydrodynamic clutches. Preferably, it is utilized on hydrodynamic clutches whose operating chambers can be emptied during operation of the clutch.
In order to achieve the function of filling degree recognition and utilization of the appropriately produced signals, especially pressure signals for triggering the device which is intended to influence the operating medium supply to the operating chamber of the hydrodynamic clutch, a control unit is preferably provided. This includes at least one control device which always has at least a first input and a first output. The first input of the control device may be at least indirectly coupled with the dynamic pressure generator or sensor. The first output of the control device may be at least indirectly coupled with the device that is intended to influence the operating medium supply to the operating chamber of the hydrodynamic clutch.
At this first input therefore, the dynamic pressure produced by the dynamic pressure generator or sensor is supplied as a signal to the control unit, either directly or as a proportional value which differs with regard to the dimension from the dynamic pressure value. In the control unit, for example, a controller output Y is allocated to either the established dynamic pressure value or to a proportional value which becomes at least indirectly effective on the device that is intended to influence the operating medium supply to the operating chamber. In the most simple scenario that is consistent with the second increased pressure value, a controller output is allocated to only the input signal at the control unit. The control unit in this instance will act as a simple converter. That is, it will or will not allocate a controller output to an input signal. The controller output Y, which is provided at the output of the control unit, can then either become directly or indirectly effective on an actuator of the device that is intended to influence the operating medium supply volume to the operating chamber of the hydrodynamic clutch. Controller output Y may be an electric, hydraulic or pneumatic, as well as a mechanical value.
These functions that are performed by the control unit can be achieved either by an appropriate selection of components and their coupling, or through a suitable microprocessor control unit. In order to perform the basic function, that is, recognition of the filling degree and triggering of the device that is intended to influence the operating medium supply volume to the operating chamber of the hydrodynamic clutch, at least two pressure switch units can be provided.
One pressure switch device each is allocated to a rotational direction of the clutch and thereby to an opening area on the dynamic pressure generator or sensor. The pressure switches assume the task of electrically triggering the actuator of the device that is intended to influence the operating medium supply volume to the operating chamber of the hydrodynamic clutch. Each pressure switch unit includes a switch which effects the corresponding coupling. In the first operating position of the pressure switch, generally when a fill signal is present, the actuator for the device that is intended to influence the operating medium supply volume to the operating chamber is triggered so that operating medium may enter the operating chamber. The release of the supply line to the operating chamber may also be continuously adjustable. Based on the pressure signal from the dynamic pressure generator or sensor, the switch is moved into the second operating position. In this second operating position, the device that is intended to influence the operating medium supply volume to the operating chamber of the hydrodynamic clutch is moved into an operating position in which the operating medium supply to the operating chamber is reduced or interrupted.
This indirect coupling arrangement between the individual pressure switch units and the actuator for the device that is intended to influence the operating medium supply volume to the operating chamber of the hydrodynamic clutch represents the minimum required equipment necessary to realize the control functions of the overfill protection. In addition, an interlock can be provided in the control circuit which can short circuit the line which connects the device that is intended to influence the supply volume into the operating chamber, possibly turning it off. That is, the actuator is no longer energized.
The switches of the pressure switch unit are triggered directly through the dynamic pressure that is produced by the dynamic pressure generator or sensor. This means that either the dynamic pressure directly, or a proportional value, becomes active at the switch and operates it. However, the first option is preferable.
A further preferred arrangement of the control unit includes at least one delay unit in the form of a time-delay relay which is installed downstream from the individual pressure switch units. This means that the device that is intended to influence the operating medium supply volume to the operating chamber of the hydrodynamic clutch, i.e., the fill valve, is switched with a certain time delay when an appropriate signal that corresponds to the maximum filling degree occurs. This is in order to prevent overfilling during a short-term pressure drop at the pressure switch. The time period is selected to be as short as possible. Preferably, time periods of between 0 and 5 seconds are utilized. This time period is adjustable according to individual situations, or can be established as a default value in the design of the time delay units. Additionally, the contact functions of pressure switches may also be used for additional switching and safety functions.
A design variation with a time-delay unit, however, should preferably not be used with clutches having a regulated coolant circuit, since the automatic control could be negatively affected.
It is also possible to install the pressure switch units directly in line with the filling valve. However, with this arrangement, the device that is intended to influence the operating medium volume to the operating chamber of the hydrodynamic clutch is activated even during short pressure drops at the pressure switch unit, thereby refilling operating medium in the operating chamber.
When starting up a motor, the hydrodynamic clutch may only be filled until there is signal present at one of the two pressure switch units. If, however, the operating chamber is not totally filled in spite of this, it would mean that the signal from the dynamic pressure generator or sensor subsides after a certain time period, and automatic refilling occurs.
In order to realize a defined fill of the clutch, i.e., a re-established filling degree, the device that is intended to influence the supply volume to the operating chamber, namely the fill valve, remains opened until the pressure switch unit reacts. Then, operation at normal rating is anticipated, and possibly a refill is made when the dynamic pressure generator or sensor signal drops to the first pressure value. In addition, the drain valve, that is, the device that is intended to influence the drainage volume from the operating chamber, is opened in a timed manner until the pressure switch unit no longer triggers the device that is intended to influence the supply volume. The filling valve is then again operated sequentially until the fill level recognition triggers again, that is, the dynamic pressure generator or sensor produces the second pressure value. By continuously monitoring the filling degree, and by continuous reaction to the filling degree, it is ensured that the desired defined filling degree is regulated. The defined filling degree that is to be determined, however, depends on the position of the dynamic pressure generator or sensor, particularly on the opening area in the accumulation chamber. The position of the dynamic pressure generator or sensor in the accumulation chamber, or their opening area relative to the accumulation chamber, always determines a firmly defined, maximum permissible filling degree. In general, this corresponds to the maximum permissible fill level of 100%. It can, however, also describe an established partial filling degree. An adjustability of the maximum permissible filling degree is also possible, by arranging the dynamic pressure generator or sensor adjustable in the accumulating chamber.
On some clutch arrangements, a coolant circuit is utilized with the operating chamber during continuous operation for the purpose of cooling. In other words, a part of the operating medium is released from the operating chamber during operation and is again returned to it through a circuit arrangement whereby a supply and drainage line can always be connected to this circuit, i.e., by use of appropriate valve arrangements, for the purpose of volumetric cooling. In such clutch arrangements, the drainage valve in the discharge from the operating chamber of the hydrodynamic clutch is first opened following triggering of the temperature monitoring unit for the operating medium exchange and the fill valve is closed after a preset time period, which can also be zero. In this scenario, operating medium is taken from the operating circuit, and at the same time, or after a very short time delay, new and cooled operating medium is added. If the signal for the filling degree condition recognition reacts during this operating medium exchange, in other words, if a second increased pressure value is produced at the dynamic pressure generator or sensor, then the device that is intended to influence the supply volume into the operating chamber, i.e., the fill valve, closes for the still set time in order to avoid overfilling. If the temperature has dropped off below an acceptable limit, the clutch is filled again. That is, the device that is intended to influence the operating medium supply volume to the operating chamber is switched so that the operating medium supply is coupled with the operating chamber. The fill valve is again closed after occurrence of a signal for the second pressure value and the condition recognition unit.
In order to accomplish the individual control tasks, the response time, the power consumption as a time function, and the operating medium temperature can additionally lead to fault indications or warnings which must be considered as additional input values for triggering the actuator of the individual valves. Additionally, the clutch fill time can also lead to a message when a certain pre-established value is exceeded.
The valve devices influencing the cross section that is to be released in the supply or drainage line of the operating chamber, can be operated mechanically, electromotively, electromagnetically, hydrostatically or pneumatically. In order to trigger the actuators, at least one signal converter is to be provided between the dynamic pressure generator or sensor and the actuator.